While snow fell in some Midwestern states Tuesday — nearly 2 feet in South Dakota's Black Hills — a strong storm system expected to drop rain along the East Coast and snow from Missouri to Michigan developed in Mississippi, Georgia and Louisiana, among other southern states. The storms in the South generated likely tornadoes, damaged some buildings and left thousands without power.

Meteorologists predicted rain-into-snow for parts of the Great Lakes region, with several inches of Christmas Eve snow expected in portions of Illinois. Officials at both airport hubs in the nation's third-largest city readied for the potential of holiday delays and cancellations, particularly with more people expected to fly this year.

"I'd be nervous about the possibility of not being able to get out," said Chicago area meteorologist Charles Mott. "I would definitely make plans about possibly staying put or doing something else."

About 4.2 million passengers are expected through O'Hare and Midway international airports during an 18-day holiday travel period ending Jan. 6, said Chicago Aviation Department spokeswoman Karen Pride. That would be a 3 percent increase at O'Hare and a 9 percent jump at Midway compared to last year. Pride urged travelers to allow plenty of time and monitor airlines closely.